The glaucomas are a common group of blinding conditions usually associated with elevated intraocular pressure. This elevated pressure in the eye may be regarded as a disorder of the drainage system of the eye which gives rise to the glaucomas.
Aqueous humor of the eye (“aqueous”) is a flowing liquid fluid (composed of sodium, chloride, bicarb, amino acids, glucose, ascorbic acid, and water) that is actively secreted by the ciliary body and flows out past the iris into the anterior chamber (are between the lens/iris and the cornea). The aquoeus drains out through angle formed by the iris and the sclera into a meshwork call the trabeculum, and from there into the canal of Schlem and then into the episcleral veins. Uveosclera drainage also occurs. Normal intraocular pressure (IOP) of aqueous in anterior chamber is between 10 and 20 mm Hg. Prolonged IOPs of greater than 21 mm Hg are associated with damage to optic nerve fibres.
In some cases of glaucoma the cause can be found: the trabecular meshwork becomes blocked by pigment or membrane. In other cases, blockage is due to a closure of the angle between the iris and the cornea. This angle type of glaucoma is referred to as “angle-closure glaucoma”. In the majority of glaucoma cases, however, called “open angle glaucoma”, the cause is unknown.
Elevated intraocular pressure results in the death of retinal ganglion cells (which convey retinal information to the brain) resulting in a characteristic pattern of loss of the field of vision, progressing to tunnel vision and blindness if left untreated.
Treatment of glaucoma consists predominantly of methods to lower the intraocular pressure (pharmacological, trabecular meshwork laser and surgery to drain fluid from the eye). More recently protection of the retinal ganglion cells by neuroprotective agents has been attempted.
Although pharmacological treatments of glaucoma have improved, they have important implications for the patient's quality of life, have compliance issues which are important in the elderly (in whom glaucoma is prevalent), expose the patient of glaucoma to side effects, and over a lifetime are costly.
Surgery for glaucoma treatment is usually a trabeculectomy in which a fistula is created to drain fluid from the anterior chamber to the subconjunctival space near the limbus, creating a bulge in the conjunctiva known as a bleb. Frequently scarring occurs and attempts to counter this with antimetabolites such as Mitomycin C have met with some success. In recalcitrant cases, glaucoma implants, drainage, shunt or valve devices have been developed eg Molteno (U.S. Pat. No. 4,457,757), Krupin (U.S. Pat. No. 5,454,746) and Baerveldt (U.S. Pat. No. 5,178,604). These suffer from similar problems of scarring (Classen L, Kivela T, Tarkkanen “A Histopathologic and immunohistochemical analysis of the filtration bleb after unsuccessful glaucoma set on implantation” Am J Ophthalmol, 1996;122:205-12) around the external opening of the tube devices in the subconjunctival space—the development of a large number of these devices is testament to the fact that many fail in the longer term. In these devices a drainage tube is located in the anterior chamber and is in fluid communication with the sclera or a surgically created subconjunctival space.
Whereas cataract surgery has been revolutionized in the last two decades, improvements in glaucoma surgery have been slower. Antifibrotic agents have improved the success rate of conventional filtration surgery (trabeculectomy), but with increased bleb leaks, blebitis, endophthalmitis and hypotensive maculopathy. Glaucoma shunts have had limited success in eyes that have “failed” multiple standard procedures. However complications with malpositioned tubes, erosion & strabismus persist. A considerable issue is the lack of reproducibility and predictability in achieving the desired target intraocular pressure (IOP). Final IOP is largely determined by healing which can be unpredictable—in view of vast biological variations, it is impossible to predict which eyes will rapidly scar causing failure and which will fail to heal resulting in prolonged post-operative hypotony. Scarring remains a significant problem in all these external drainage proposals, where aqueous drains into the conjunctiva, or surgical chambers in the sclera.
The introduction of a new class of antiglaucoma drugs, the prostaglandin analogues has resulted in acknowledgment of the importance of the uveoscleral pathway in drainage of fluid form the eye (Hylton C, Robin A L “Update on prostaglandin analogs” Curr Opin Ophthalmol, 2003;14:65-9). Uveoscleral flow where aqueous humor flows through the interstitium of the ciliary muscle into the suprachoroidal space (a potential space between the choroids and sclera) and out through the sclera into the connective tissue of the orbit may account for 54% of outflow young healthy humans (Toris C B, Yablonski M E, Wang Y L, Camras C B “Aqueous humor dynamics in the aging human eye” Am J Ophthalmol, 1999;127:407-12).
Cyclodialysis, the separation of the ciliary body from the scleral spur and underlying sclera, creates free communication between the anterior chamber and the suprachoroidal space and enhances uveoscleral flow. It has long been known that cyclodialysis can cause a profound reduction of intraocular pressure—initially (Fuchs E. “Detachment of the choroid inadvertently during cataract surgery” [German] von Graefes Arch Ophthalmol, 1900;51:199-224) cyclodialysis was recognized as a complication of cataract surgery. Deliberate creation of a cyclodialysis cleft for treating elevated intraocular pressure in uncontrolled glaucoma was first described as a surgical procedure in 1905 (Heine I. “Cyclodialysis, a new glaucoma operation” [German]) Dtsch Med Wochenschr, 1905;31:824-826. Since such clefts can heal and close spontaneously a number of devices have been used to keep them open, including platinum wire, horse hair, magnesium strips, tantalum foil, supramid, gelatin film, Teflon, silicone and polymethylmethacrylate (Rosenberg L F, Krupin T. “Implants in glaucoma surgery” Chapter 88, The Glaucomas, Ritch R, Shields B M, Krupin T Eds. 2nd Edition Mosby St Louis 1986) and Hema (Mehta K R. “The suprachoroidal Hema wedge in glaucoma surgery” American Academy of Ophthalmology meeting 1977, pp 144). However the success rate of such approaches has been low (as low as 15%, Rosenburg & Krupin ibid and Gross R L, Feldman R M, Spaeth G L, et al “Surgical therapy of chronic glaucoma in aphakia and pseudophakia” Ophthalmology, 1988;95:1195-201). Failure was due to uncontrolled low pressure (hypotony) with consequentiqal macular edema, bleeding (hyphema) and inadequate pressure control.
The device and method of a first aspect of this invention takes advantage of the methods used in cataract surgery to develop a minimally invasive glaucoma procedure—thus small, self sealing incisions and materials that are biocompatible and fodable so that they fit through small openings will reduce surgical trauma and time. The controlled draining of aqueous into the suprachoroidal space according to this invention provides some predictability of outcome and overcomes scarring problems that have plagued glaucoma implants in the past.
The most frequent complication following modern cataract surgery with phacoemulsification, requiring specific treatment is elevated intraocular pressure (Cohen V M, Demetria H, Jordan K, Lamb R J, Vivian A J. :First day post-operative review following uncomplicated phacoemulsification” Eye, 1998;12 (Pt 4):634-6, and Dinakaran S, Desai S P, Raj P S. “Is the first post-operative day review necessary following uncomplicated phacoemulsification surgery?” Eye, June 2000; 14 (Pt 3A):364-6. The increase may be marked and typically peaks at 5 to 7 hours before returning to near normal levels in 1 to 3 days (Hildebrand G D, Wickremasinghe S S, Tranos P G, Harris M L, Little B C. “Efficacy of anterior chamber decompression in controlling early intraocular pressure spikes after uneventful phacoemulsification” J Cataract Refract Surg., 2003; 29:1087-92). Such pressure spikes can cause pain and may increase the risk of sight-threatening complications such as retinal vascular occlusion, increases loss of visual filed in advanced glaucoma and ischemic optic neuropathy—effects in otherwise healthy eyes are unknown (Hildebrand G D et al, ibid).
A number of prophylactic treatments are used with limited success—these include intacameral carbachol or acetylcholine, topical timolol, dorzolamide, aproclonidine, latanoprost and systemic acetazolamide (see Hildebrand G D et al, ibid). This also exposes the patient to the risk of drug side effects, increased cost and it has been postulated that reducing the flow of aqueous humor post surgery prolongs the residence time of bacteria that frequently (46.3% of cases) contaminate the anterior chamber during surgery (Srinivasan R, Tiroumal S, Kanungo R, Natarajan M K. “Microbial contamination of the anterior chamber during phacoemulsification” J Cataract Refract Surg, 2002; 28:2173-6.). This may increase the risk of endopthalmitis one of the most devastating sequeleae of intraocular surgery, since the bacteria are not being “flushed out” of the eye by the normal production of aqueous humour, the secretion of which has been suppressed by the drugs. Another technique is to decompress the anterior chamber by applying pressure to the posterior lip of the paracentesis wound at the appropriate time. This requires surveillance and could increase the risk of infection. Another aspect of this invention hereinafter described overcomes these problems.